Heretofore, there have been attempts to control traveling of a vehicle in a traffic flow, thereby improving traffic on a road and reducing a traffic jam. For example, a case where communication system-mounted vehicles which are communicable with other vehicles by vehicle-to-vehicle communication are included in a traffic flow at a predetermined ratio is considered. In this case, the communication system-mounted vehicles share information on vehicle speed or current positions and perform collaborative traveling control, thereby indirectly controlling the motions of vehicles therebetween and effectively reducing a traffic jam. In the traveling control in collaboration with other communication system-mounted vehicles, it is necessary for each communication system-mounted vehicle to specify other communication system-mounted vehicles with which to collaborate.
That is, it is necessary for the communication system-mounted vehicle to acquire positional information of other communication system-mounted vehicles. As a technique for acquiring positional information of other vehicles, an another vehicle position detection device described in Patent Literature 1 is known. The position detection device calculates the difference between the received GPS coordinates in the host vehicle and the position coordinates after correction in the host vehicle calculated by map matching as a GPS error, and corrects the GPS coordinates acquired from another vehicle using the GPS error to calculate the accurate position of another vehicle.